Biomass encompasses a wide array of organic materials including wood, woody waste, agricultural residues, and crops grown specifically for energy production. The U.S. alone generates billions of tons of biomass annually. Beneficiated biomass, in which the moisture content has been reduced and the energy density has been increased, can be used as a feedstock for several products, including pellets for residential heaters, hydrocarbon liquid fuels, cellulosic ethanol, solid fuel to supplant coal, or for production of synthetic natural gas.
Beneficiation is the treatment of raw material to improve physical or chemical properties and typically includes steps to increase the energy density. Conventional methods to beneficiate biomass include heat/steam treatment, torrefication, and pressure extrusion (“densification”). These methods have not been designed necessarily to remove entrained salts.
As an alternative, a re-designed heat/steam treatment of biomass materials with additional cleaning steps can substantially improve the quality of densified biomass while also reducing the amount of required energy. Heat/steam treatment has a variety of descriptions and methods in the literature and centers on biomass drying and energy densification. Most heat/steam systems dry the material early in the process, even before the heat/steam process.
Steam-exploded beneficiated biomass, in which the plant fibers are disrupted and the sugars associated with cellulose and hemicellulose are made more available to plant-supporting micro-organisms, can be used as an engineered soil, or soil supplement. As an alternative to peat, steam exploded biomass materials can substantially improve the quality of biomass for engineered soil producing a loosely packed, peat-like material. The beneficiated biomass resembles peat in its composition and usefulness, thereby preserving endangered peat bogs, which can take centuries to recover from harvesting. The process of the present invention produces a material very similar in composition to peat moss.
Thus, there is a need for beneficiation methods to further remove entrained salts and light volatiles from biomass materials. It may also be desirable to minimize energy use through capturing steam and flue gases for re-use. It also may be desirable to use treated biomass materials as an engineered soil.